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The World Needs Less Inline-Four Engines

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The World Needs Less Inline-Four Engines

Without a doubt, Mercedes-Benz made the biggest splash over the past week with the announcement of four new engines, two of which were inline-sixes, the first such powerplants for the brand in two long decades of hammering out dull V6 engines. Not only that, the petrol-powered inline-six in particular was built with the latest 48-volt high-voltage system, which means that it can power a lag-cutting electrically-powered turbocharger.  

Better yet, amongst the quartet of new engines, there was only one four-banger in the line-up, whereas the other is an ‘AMG-developed’ V8 engine. Although exact numbers on the new four-potter petrol is scarce, with its specific power output touted as ‘100kW per litre’ from its 2-litres of displacement, there is bound to be different versions with varying degrees of power outputs to appeal to a broad spectrum of buyers.

For the time being, that four-cylinder will be the subject of discussion for another day. In the meantime, there is reason to celebrate the return of an inline-six engine to Mercedes-Benz’s fold. As this Road & Track article explains, while a V6 makes dollars and cents sense - often for sharing a modular design with a V8 engine - and easier to shoehorn into a variety of engine bays, an inline-six is still the engineer’s choice for its inherent smoothness.

Very rarely do engineers get to have their way in delivering an engine that they want these days, as boardroom lingo like product synergy or managing costs often permeate through the ranks. Hopefully we are at the cusp of a new age of engines as head of Mercedes-Benz Cars development, Dr Thomas Weber describes the new engine family as being built on the ‘rightsizing’ bandwagon, as opposed to the ‘downsizing’ movement that had dictated the trends of the automotive industry of the last few decades.

Downsizing had seen the end of big displacement engines in favour of tiny turbocharged four-cylinder engines. BMW’s mainstay went from inline-sixes to turbocharged four-cylinder mills within a model update. Volvo killed off its beguiling inline-five for a twincharged inline-four. And even Jaguar, who were still valiantly cramming supercharged V8s into everything they had, thought it was a good idea to have a hybrid-supercar with only four cylinders to pull its weight. One by one, engines with more than a quartet of cylinders were eliminated like the Dodo, turned into an anachronism in a new age of emissions and soaring fuel prices.

While there is no denying that the turbo-torque of these downsized engines did make urban commuting - and racing between the lights - a whole lot enjoyable, most inline-four engines are devoid of character. Built for economy, with the minimum amount of cylinders required to achieve operational smoothness, the inline-four is more of a necessity than any flight of fancy ingenuity or imagination.

There are of course a handful of great straight-four engines that occupy my waking thoughts to this day. Honda’s VTEC-banzai performance engines immediately come to mind for its frenetic power delivery, whereas Alfa Romeo’s sonorous Twinspark engines was the Pavarotti of its kind. But besides those examples - that aren’t around anymore due to tight emission regulations - and a few other luminaries, there aren’t many current inline-four engines out there that pique my interest, especially in today’s age of turbocharging.

Although big engines will continue to be the reserve of the more opulent or high-performance variants, affordable cars for the rest of us proletariats doesn’t have to put up with the mundanity of the inline-four. After all, considering that some of the loveliest engines I’ve had the good fortune of trying had an odd number of cylinders.

The five-cylinder engine in the previous Audi TT RS made it the polar opposite of the Renault Megane RS, an engine that was as brilliant and charming as the Megane RS’ handling from a car that had was as drab and dreary as the French car’s engine note. In a way, it is also the same story with Volvo’s now discontinued five-potter. For some strange reason the S60 in its T4 guise, with its Mondeo Ecoboost-derived four-cylinder, had better handling. But despite its nose-heaviness and numb steering, the addictive offbeat thrum when you gun that inline-five engine made the T5 variant all the more endearing for it.

Even if you were to insist on downsizing engines, dropping a cylinder seems to make things a whole lot better, as is the case with BMW’s current 1.5-litre three-cylinder unit, or Ford’s 1-litre Ecoboost mill. Both engines might give a healthy slug of torque for a quick pick-up. But unlike an inline-four engine, when you push on harder it buzzes like nest of angry hornets all jacked up on methamphetamine.


Sure a Fiesta with the 1-litre Ecoboost, or a MINI Cooper with the 1.5-litre engine, doesn’t bolt off from the lights as quickly as the Fiesta ST and MINI Cooper S, but working that engine feels all the more rewarding. It feels like a small Terrier snarling at anything two sizes bigger than it, punching above its weight and reveling in the moment.

It is that enthusiastic personality or warbling soundtrack that you wouldn’t find in today’s crop of inline-fours. These days I will be hard pressed to think of a modern inline-four engine that I actually find desirable. They may be immensely powerful like the 350PS inline-four in the Focus RS, efficient, and easy to maintain, but none really tugs at my heartstrings enough for me to univocally say “Yes! This! In my garage! Now!” while pawning off anything in the living room that isn’t bolted down.

But there is no reason for manufacturers to move on from the good ol’ straight-four, considering the easy to which it can fit into any layout, and be paired with any number of drivetrain combinations. Whereas there is relatively little power gains or engineering advantages to be had by going through all the extra trouble of adding another cylinder, and conversely it is harder to market an engine with one less cylinder as well. In the meantime, the aforementioned ‘rightsizing’ trend will see manufacturers resorting to cramming their engines with more advanced technologies such as cylinder cut-off, triple injection, or electric-turbochargers to achieve the optimal efficiency at all engine loads, rather than grow the displacement of their upcoming engines.  

As much as I hate to say it, for the foreseeable future, the inline-four is here to stay, which makes such oft-engineered engines all the more affable and unique in a world of increasing mundanity.

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